Starch from hull-less barley: I. Granule morphology, composition and amylopectin structure

Abstract

Starch was extracted from 10 hull-less barley (HB) genotypes [waxy (CDC Candle, CDC Alamo, SB 94912, and SB 94917), normal amylose (Phoenix, CDC Dawn, SR 93102, and SB 94860), and high amylose (SB 94893 and SB 94897)]. Starch content ranged from 56 to 65%. The purity of the isolated starches was greater than 96%. Average starch yield and extraction efficiency were 44 and 71%, respectively. The starches from all genotypes consisted of a mixture of large lenticular and small irregularly shaped granules. The granules of most starches were intact, whereas in others (SB 94917, SR 93102, and SB 94860) they were compound (clustered). The proportions of small (diameter⩽10 μm) and large granules (diameter>10 μm), by total number and by total weight differed among genotypes. Bound lipid content was positively correlated (r=0.92, P<0.01) with total amylose content. Free and bound lipid contents ranged from 0.1–0.3% and 0.3–1.7%, respectively. The apparent and total amylose contents ranged from 0–39% and 0–45%, respectively. The amounts of amylose complexed with native lipids (total amylose–apparent amylose) ranged from 0.5 to 7.8%. The proportion of small granules was correlated with total amylose content (r=0.59, P<0.1). However, the average granule diameter was negatively correlated (r=−0.65, P<0.05) with total amylose content. The debranched amylopectins of all starches exhibited the highest peak in the MALDI-MS spectrum at DP 12. The average chain length (CL) and degree of branching ranged from 17.6–22.7% and 4.4–5.5%, respectively. The short (DP 5-17) and long (DP⩾35) chains ranged from 58.2–59.1% and 3.0–12.8%, respectively. The study showed that amylose/amylopectin ratio and amylopectin branch chain length have high correlation with granule size and size distribution in this set of barley genotypes.